Nettie Stevens and Edmund Wilson explain how gender is determined by special chromosomes.
Hello, I'm Nettie Stevens. Dr. Edmund Wilson and I showed that gender is determined by special chromosomes. I did it by looking at cells of meal worms.
[MEAL WORM LARVA]
The following drawings are adapted from my 1905 paper. Body cells from female worms have 20 chromosomes, all similar in size. As expected, female gametes have a half set of chromosomes (10).
In male body cells, there are 19 similar chromosomes and one that is much smaller. I found that two types of male gametes are made during meiosis. Some sperm have the small chromosome, and some don't.
I concluded that the "different" chromosome must be responsible for maleness in meal worms. This different chromosome Y and its larger partner X are sex chromosomes. Gender in most species is determined by these sex chromosomes.
So, gender is inherited like a Mendelian trait. Human gender is determined this way...
Females have two X chromosomes;
Males have one X and one Y.
Since females can only contribute an X chromosome, males are responsible for the sex of offspring. They can provide either an X chromosome for a female...
XX: It's a girl!
....or a Y chromosome for a male. If meiosis and fertilization occur normally, there will be an equal number of males and females.
XY: It's a boy!
sex chromosomes, x chromosomes,y chromosomes worm larva, edmund wilson, meal worms, male gametes, nettie stevens, fertilization, body cell, gamete